Question

I am familiar with Regular Expressions, but this complex example is tripping me up. I trying to understand what this line of code is doing:

r'/(\\.|[^[/\\\n]|\[(\\.|[^\]\\\n])*])+/([gim]+\b|\B)'

It is a code snippet that is trying to detect a regular expression, for example: /\s+/. I understand it until the nested [, \[, and the ( counterparts.

(I need to port this code from Python to Java and am having problems understanding how the above works, and why it does not work as is in Java.)

Answer 1

Here’s an exploded version that might help:

/                      # Match an opening slash
(                      # Followed by one or more...
  \\.                  #    Backslash followed by any character
  |                    #   or...
  [^[/\\\n]            #    Something that's not a [, /, \, or newline
  |                    #   or...
  \[                   #    A literal [, followed by any number of...
    (
      \\.              #     backslashes followed by any character
      |                #     or...
      [^\]\\\n]        #     something that's not a ], \, or newline
    )*
  ]                    #    and ending with a ]
)+
/                      # And a closing slash
(
  [gim]+\b             # Followed by one or more of g, i, m
  |
  \B                   # or something that isn't a word boundary
)